1. Field of the Invention
The present invention relates to hydraulic construction equipment such as excavators, loaders, bulldozers and the like, and more particularly to an apparatus for and a method of controlling the engine and pumps of such hydraulic construction equipment to achieve the automation of the hydraulic construction equipment.
2. Description of the Prior Art
As is well-known, hydraulic construction equipment includes a plurality of variable displacement pumps and work implements, such as booms, arms and buckets using a plurality of hydraulic cylinders as their actuators. Manipulation of such work implements is carried out by using manipulation command means such as joy stick, pedal and lever disposed near the driver's seat. On the other hand, the speed of each work implement and the speed ratio of the work implement to each other work implements associated therewith are proportional to the manipulation amount and manipulation ratio of the manipulation command means associated with the work implement. In order to satisfy the required speed of each work implement, each pump is designed to supply a quantity of operating oil proportional to the manipulation amount of the manipulation command means.
Actually, however, the pump has a mechanical limitation of maximum delivery oil quantity. Where the work implement is electronically controlled using an electric manipulation command device and a solenoid controlled proportional valve, the sum of required pump delivery quantities corresponding to respective command values of manipulation command means for work implements and to the respective speeds of the work implements may exceed the maximum delivery oil quantity under the current load pressure, depending on the variation in load pressure caused by a variation in working circumstance in excavating, loading and leveling type work.
In such a case, when the work implements operate in combination, the actual speed ratio of each work implement to each other work implements associated therewith can not correspond to the manipulation ratio based on a corresponding manipulation command signal for the work implement in accordance with known engine-pump control methods. In other words, the speed of each work implement and the speed ratio of the work implement to each associated work implement can not correspond to the manipulation amount and manipulation ratio based on the manipulation command signal due to variations in working circumstances and load pressures. This results in degradations of workability and working efficiency. Moreover, a stall phenomenon occurs in the engine due to an overload generated in the work process.